Helicopter Forward Transitions

During the Private Pilot course a lot of students find the most difficult exercise to be the forward transition. Just to clarify if we talk about transition in a helicopter it is the phase between the hover and starting a climb or from a descend back to hover flight.

Let’s start off by looking at one aerodynamic aspect: Translational lift: This is the result of wind blowing over the disc or the helicopter moving forward (wind or forward movement between 12 to 16 knots) causing a reduction in the induced flow passing through the disc thereby causing an effective increase in the angle of attack which will result in the helicopter wanting to climb for a certain collective pitch setting.

In my opinion, to fly a proper transition is one of the more difficult exercises, because so many aerodynamic changes take place. Remember a decent transition is not what you see on a James Bond movie when the helicopter pitches the nose down accelerates to 300 knots in three seconds while wiping out the building with its blades in the process.

A “normal” safe transition is as per the Pilot Operating Handbook. The essence is to stay out of the avoid area of the height velocity diagram.

The most common factor that results in a student struggling initially with transitions is the fact that the student does not anticipate the “kick” (translational lift). So most of the time the student tries to compensate for all the aerodynamic factors that take place after it has already taken place. Take your time. You must dictate when you’re going through transition.

You are allowed to climb slightly (usually about 10 foot) as long as you don’t climb into the avoid area of the height/velocity diagram. To compensate for translational lift cyclic movement has to be gradually, constant, and continuously to compensate for FLAP BACK (BLOW BACK). Flap back does not happen just once, it’s a continuous process that occurs all the time while we accelerate, and therefore the attitude has to be lowered all the time by pushing the cyclic forward. In other words you must SEE that your attitude reference marker, whether it is the canopy or the rotor disc for example, continuously lowers (pitches towards the skids) without forcing the helicopter to descend.

Fly what you see and feel the helicopter. Get a reference point for the nose to pick up the yaw changes.

In my eBook I go into more depth regarding the forward and reverse transition.



HARRY





© Harry Helicopter Training Syllabus 2008